The use of threaded inserts, generally made of titanium, has become the dominant technology currently used for dental implant surgery. Such inserts must be precisely located in the tooth in order to provide optimum aesthetic and beneficial results. Bone preparation must be precise and should preferably be carried out with the implant site and shape in constant view of the dental surgeon. In particular, during the drilling phase of the bone preparation, great care must be taken to avoid causing injury to the patient. Examples of such potential damage include inadvertent entry into the mandibular nerve canal, possible perforation of the cortical plates, or damage to adjacent teeth.
In order to achieve these objectives, exact knowledge of the bone topology of the jaw must be on hand. Such information is today obtainable from computer-generated panoramic and oblique radiographic CT scans of the jaw, which provide the cross-sectional shape of the jaw at every point throughout the arch on a 1:1 scale. In order to use the information on such CT images optimally, the dental surgeon should be provided with a continuous, real-time, three-dimensional image of the location and direction of the drill during the drilling procedure into the bone at all times during its execution. As a result, there should be optimal correlation between the implantation planning and the actual surgical performance, and accurate placement of the insert, even by less experienced clinicians, and additionally, reduction to a minimum of any danger of damage to vital anatomical structures, such as the inferior alveolar nerve, the maxillary antrum, the nasal cavity, adjacent teeth, or cortical plates.
However, the successful and accurate implementation of a system providing such information is dependent on the accuracy of the initial input data of the CT imagery provided to the system computer. Such data as supplied by the CT scanner may generally be distorted, whether because of imperfections in the algorithms used in the scanner software, or because of interpolations made in areas where exact measurements are not performed, or simply because of inaccuracies due to excessive patient movement during the CT scan. Very high accuracy is required in dental implantology, where even a fraction of a millimeter of excess penetration or a degree or two of misalignment, can mean the difference between a successful procedure and an unsatisfactory one, or even between a safe procedure and injury to the patient. Consequently, the distortion inherent in generally available CT scans is such that such scans cannot be used as supplied, for accurate image-guided dental implantology.
There therefore exists a serious need for a method of compensating or correcting for such CT distortion for use in image-guided implantation surgery. In addition, such a method would also be applicable and necessary for use in other accurate, image-guided surgical or industrial procedures which utilize scanned image information for determining an exact overall picture of the imaged subject or object.
Furthermore, even if such accurately corrected CT imagery were available, it is necessary to relate the computer-generated virtual images of the patient's jaw with the actual teeth in the patient's jaw, and with the position of the dental surgeon's hand and drill. Thus, it is necessary to correlate a definite point on a CT scan with its matching point in the patient's jaw, and a stereometric angle on the scan with the corresponding angle in the patient's jaw. Without such correlation, even the most accurate and undistorted CT scan is of very limited use for guiding any sort of real time surgical procedure, such as implant preparation. Furthermore, the correlation must take into account and track any motion of the patient's jaw during the procedure. In U.S. Pat. No. 5,842,858 to M Truppe, for “Method of Imaging a Person's Jaw and a Model thereof”, there is described a method whereby such correlation and tracking are performed using a 3-D sensor attached, for instance by means of screws, to the outside of the jaw of the patient, which is referenced by means of a tracking system to another 3-D sensor temporarily located inside the jaw. Such a referencing method may be considered disadvantageous since it entails subject involvement, and may also be dependent on operator skill in attachment of the 3-D sensor to the outside of the patient's jaw. Furthermore, physiological changes taking place in the tissue and muscle of the patient's jaw during the course of the procedure may induce inaccuracies in the position of the sensor. These factors may compromise the high accuracy required for an accurate implant procedure.
There therefore exists a serious need for a method of correlating virtual CT images previously obtained of a patient's jaw with the actual situation being followed by the drill in real time in the patient's jaw during a dental surgical procedure. The method should ideally be performed with minimal interaction with the patient's jaw, in order to reduce subjective inaccuracies as much as possible. Furthermore, it should be simple enough to be executable by personnel other than the dental surgeon himself, such as a dental technician. It is to be understood that such a method would also be useful and applicable in other accurate, image-guided surgical or industrial procedures which utilize scanned image information for determining the overall picture of a real-time procedure being performed.
The disclosures of all publications mentioned in this section and in the other sections of the specification, are hereby incorporated by reference, each in its entirety.